Ozone is widely used in the disposal of waste water or for purifying air, and is particularly used for the decomposition of organic compounds because of its high oxidizing power. Ozone has heretofore been commercially produced for many years by the discharging method. The discharging method produces ozone by an electric discharge, such as silent discharging in air or oxygen. In this method, however, dry oxygen is needed for production of high concentration ozone or high concentration ozone water, and consumption of the electrode leads to contamination of ozone with the electrode substance, although the electric power consumption is relatively low. Where ozone is used in the production of super pure water for electronics applications or the removal of photoresist materials, contamination of the ozone is highly undesirable. In order to overcome the above problems associated with the discharging method, an electrolyzing method whereby contamination with impurities is reduced although the electric power consumption is increased to several times that of the discharging method has been receiving attention in recent years. Moreover, wet, high concentration ozone is readily obtained by the electrolyzing method.
In the production of ozone by the electrolyzing method, an electrode having a high oxidizing ability, e.g., lead oxide is employed to electrolyze water, as described in U.S. Pat. No. 4,416,747. A plurality of small-sized electrolytic cells are usually placed together and electrolysis is carried out concurrently. This electrolyzing method can comprise a bipolar-electrode type or a monopolar-electrode type, depending on the method employed for supplying current to the electrodes.
The bipolar-electrode method employs a plurality of electrolyzing cells electrically connected in series, i.e., anode - cathode - anode - cathode - anode - cathode. Although the voltage applied thereto is large, the current usage is small. Electrical connection to the electrodes is thereby facilitated and current is uniformly distributed to the electrolytic cells. In the bipolar-electrode electrolytic cell, however, if the electrolytic compartments of each electrolytic cell are connected by conduits, a stray leakage current arises which bypasses the electrolytic solution. Even though the electrolytic solution is substantially insulating, the stray current causes a reduction of efficiency and corrosion of valves, piping and other facility components.
In order to eliminate the above problems, in the conventional bipolar-electrode type electrolytic cells, electrolyte liquids in adjacent electrode (anode and cathode) compartments are strictly separated to prevent leakage current. This separation system, however, takes away from the desirable features of the bipolar-electrode system (i.e., simple and inexpensive apparatus). Even when the electric resistance of the electrolytic solution is large, the electrolyte separation is still carried out taking the leakage current overly into account, and the apparatus is complicated.
The present inventors have proposed ozone electrolysis by the SPE method (Japanese Patent Application Nos. 297673/1987, 297674/1987 and 297675/1987). Even in the bipolar-electrode type electrolytic cell using the SPE method, the same problems as noted above occur.